The Tor Project on browser fingerprinting and how it is taking a stand against it

In a blog post shared on Wednesday, Pierre Laperdrix, a postdoctoral researcher in the Secure Web Applications Group at CISPA, talked about browser fingerprinting, its risks, and the efforts taken by the Tor Project to prevent it. He also talked about his Fingerprint Central website, which is officially a part of the Tor project since 2017.

What is browser fingerprinting

Browser fingerprinting is the systematic collection of information about a remote computing device for the purposes of identification. There are several techniques through which a third-party can get a “rich fingerprint.” These include the availability of JavaScript or other client-side scripting languages, the user-agent and the accept headers, HTML5 Canvas element, and more.

The browser fingerprints may include information like browser and operating system type and version, active plugins, timezone, language, screen resolution and various other active settings. Some users may think that these are too generic to identify a particular person. However, a study by Panopticlick, a browser fingerprinting test website, says that only 1 in 286,777 other browsers will share its fingerprint.

As with any technology, browser fingerprinting can be used or misused. The fingerprints can enable a remote application to prevent potential frauds or online identity thefts. On the other hand, these can also be used to track users across websites and collect information about their online behavior, without their consent. Advertisers and marketers can use this data for targeted advertising.

Steps taken by the Tor Project to prevent browser fingerprinting

Laperdrix said that Tor was the very first browser to understand and address the privacy threats browser fingerprinting poses. The Tor browser, which goes by the tagline “anonymity online”, is designed to reduce online tracking and identification of users.

The browser takes a very simple approach to prevent the identification of users. “In the end, the approach chosen by Tor developers is simple: all Tor users should have the exact same fingerprint. No matter what device or operating system you are using, your browser fingerprint should be the same as any device running Tor Browser,” Laperdrix wrote.

There are many other changes that have been made to the Tor browser over the years to prevent the unique identification of users. Tor warns users when they maximize their browser window as it is also one attribute that can be used to identify them. It has introduced default fallback fonts to prevent font and canvas fingerprinting. It has all the JS clock sources and event timestamps set to a specific resolution to prevent JS from measuring the time intervals of things like typing to produce a fingerprint.

Talking about his contribution towards preventing browser fingerprinting, Laperdrix wrote, “As part of the effort to reduce fingerprinting, I also developed a fingerprinting website called FP Central to help Tor developers find fingerprint regressions between different Tor builds.”

As a part of Google Summer of Code 2016, Laperdrix proposed to develop a website called Fingerprint Central, which is now officially included in the Tor Project. Similar to AmIUnique.org or Panopticlick, FP Central is developed to study the diversity of browser fingerprints. It runs a fingerprinting test suite and collects data from Tor browsers to help developers design and test new fingerprinting protection. They can also use it to ensure that fingerprinting-related bugs are correctly fixed with specific regression tests.

Explaining the long-term goal of the website he said, “The expected long-term impact of this project is to reduce the differences between Tor users and reinforce their privacy and anonymity online.”

There are a whole lot of modifications made under the hood to prevent browser fingerprinting that you can check out using the “tbb-fingerprinting” tag in the bug tracker. These modifications will also make their way into future releases of Firefox under the Tor Uplift program.

Many organizations have taken a step against browser fingerprinting including browser companies Mozilla and Brave. Earlier this week, Firefox 69 was shipped with browser fingerprinting blocked by default. Brave also comes with a Fingerprinting Protection Mode enabled by default. In 2018, Apple updated Safari to only share a simplified system profile making it difficult to uniquely identify or track users.